The VG on top(1"x1"x1/8"x1'-1.5'aluminum angle) have a blunt front and rear (rectangular). There orientation is in the direction of travel. Travel and air flow direction seldom match at the rear especially at corners.
The fronts should be curved from bace up and back. Parallelogram with curved leading and trailing edges. Not like the side VGs.(trapezoid)
This is a poor example with witch to condemn all VGs. Poor fit and finish .In my opinion.
1st gen cummins 91.5 dodge d250 ,16cm turbo housing exost manafulld wrap, Aero Cap
best tank: distance 649gps mi 24.04 mpg27.011
Best mpg : 29.3mpg
97mi 3.311usg 7/27/16